The present invention relates to cells and cell growth, and in particular to mammalian cells and autocrine factor.
The epithelium consists of the membranous tissue that covers the internal and free surfaces of the human body. In conjunction with associated cell systems, epithelial cells function primarily in the areas of enclosure, protection and assimilation. Among the biologically relevant human cell systems is the epidermal keratinocyte, which represents the predominant cell type within the skin epithelium.
Clonal growth of normal human keratinocytes can be achieved in a defined (e.g., serum-free) medium as described by Boyce and Ham, J. Invest. Dermatol., Vol. 80, p. 33s (1983); Shipley and Pittlekow, Arch. Dermatol, Vol. 123, p. 1541a (1987); and in the absence of fibroblast feeder layers or extracellular matrix as described by Rheinwald and Green, Cell, Vol. 6, p. 331 (1975); Peehl and Hamm, In Vitro Cell. Dev. Biol., Vol. 16, p. 516 (1980); Tsao et al., J. Cell. Physiol., Vol. 110, p. 219 (1982). Moreover, the level of proliferative activity and the extent to which cultured keratinocytes terminally differentiate are thought to be inversely related such that the presence of exogenous medium components (e.g., epidermal growth factor), and such that a reduced concentration of extracellular calcium greatly favors cell growth. See Boyce and Hamm, J. Invest. Dermatol., Vol. 81, p. 33a (1983); Wille et al., J. Cell. Physiol., Vol. 121, p. 31 (1984); Pillai et al., Cell. Physiol., Vol. 134, p. 229 (1988). It is also believed that keratinocyte proliferation may be influenced by an autocrine mechanism, and therefore less dependent upon the exogenous components traditionally used to supplement growth medium preparations. See, Cook et al., J. Cell. Physiol., Vol. 146, p. 277 (1991) and Cook et al., Molec. Cell Biol., Vol. 11(5), p. 2547 (1991).
It would be desirable to produce autocrine factor responsible for cell growth, and to provide efficient and effective methods for growing those cells which rely upon autocrine signalling.